Glutamine stimulates growth in rat cerebral endothelial cell culture

Cerebromicrovascular endothelial cells are resistant to L-glutamate

Cerebral microvascular endothelial cells (CMVECs) have recently been implicated as targets of excitotoxic injury by l-glutamate (l-glut) or N-methyl-d-aspartate (NMDA) in vitro. However, high levels of l-glut do not compromise the function of the blood-brain barrier in vivo. We sought to determine whether primary cultures of rat and piglet CMVECs or cerebral microvascular pericytes (CMVPCs) are indeed sensitive to l-glut or NMDA. Viability was unaffected by 8-h exposure to 1-10 mM l-glut or NMDA in CMVECs or CMVPCs isolated from both species. Furthermore, neither 1 mM l-glut nor NMDA augmented cell death induced by 12-h oxygen-glucose deprivation in rat CMVECs or by 8-h medium withdrawal in CMVPCs. Additionally, transendothelial electrical resistance of rat CMVEC-astrocyte cocultures or piglet CMVEC cultures were not compromised by up to 24-h exposure to 1 mM l-glut or NMDA. The Ca(2+) ionophore calcimycin (5 microM), but not l-glut (1 mM), increased intracellular Ca(2+) levels in rat CMVECs and CMVPCs assessed with fluo-4 AM fluorescence and confocal microscopy. CMVEC-dependent pial arteriolar vasodilation to hypercapnia and bradykinin was unaffected by intracarotid infusion of l-glut in anesthetized piglets by closed cranial window/intravital microscopy. We conclude that cerebral microvascular cells are insensitive and resistant to glutamatergic stimuli in accordance with their in vivo role as regulators of potentially neurotoxic amino acids across the blood-brain barrier.

Amelioration of hypoxic and hypoglycemic damage to cerebral endothelial cells. Effects of heat shock pretreatment

Induction of the 70 kDa heat shock protein (HSP70) by hypoxia and/or hypoglycemia and the effects of prior heat shock on injury owing to hypoxia and/or hypoglycemia were studied in rat cerebral endothelial cells. Hypoxia and/or hypoglycemia treatment resulted in increased expression of HSP70 only when such treatment was sufficient to cause detectable injury and when the initial treatment was followed by exposure of the cells to 24 h of normoxia and normoglycemia. Heat shock induced 24 h prior to treatment with 48 h of hypoxia slightly reduced endothelial cell damage as measured by fraction of lactate dehydrogenase release (10% decrease in injury). There was a more dramatic effect of prior heat shock on the moderate damage produced by 12 h of combined hypoxia and hypoglycemia (45% decrease), whereas the severe damage produced by 24 h of hypoxia and hypoglycemia was decreased by prior heat shock by only 16%. These results indicate that the hypoxia and hypoglycemia occurring in conjunction with ischemia are more likely to result in heat shock protein expression when there is injury to the tissue. Furthermore, heat shock protects cerebral endothelial cells from hypoxia and hypoglycemia either by slowing the initial development of injury or by delaying the onset of injury.

Carrier-mediated uptake and release of histamine by cultured rat cerebral endothelial cells

The present study demonstrates that histamine could be taken up by and released from endothelial cells of brain capillaries. Incubation of cultured endothelial cells, with low (0.01-0.50 microM) concentrations of [3H]histamine, resulted in a rapid uptake of the amine. The uptake was saturable, Na(+)-dependent and yielded an apparent Km 0.3 +/- 0.02 microM and a Vmax 4.6 +/- 0.04 pmol/mg protein per min. After a 10-min incubation in a histamine-free medium, about 65% of [3H]histamine was released from the cells. Na(+)-deprivation and high K+, as well as the treatment of the cells with ouabain affected the release, resulting in significantly higher rates of the efflux. The ability of cerebral endothelial cells to take up histamine from both luminal and abluminal sides but to release it mainly luminally, may function as an important mechanism to protect the neural tissue from the harmful effects of this endogenous mediator of inflammation.

Fluid-phase endocytosis of horseradish peroxidase by cerebral endothelial cells in primary culture: characterization and kinetic analysis

Endocytosis of horseradish peroxidase (HRP) was studied in primary cultures of cerebral endothelial cells prepared from 2-week-old rats. These cultures were considered "endothelial-like" on the basis of their ability to internalize acetylated low density lipoprotein. Cellular localization of HRP protein was examined at the light and ultrastructural levels and endocytosis of the protein was evaluated by a colorimetric assay. HRP was localized in discrete cytoplasmic granules by light microscopy. At the ultrastructural level these granules corresponded to pleomorphic membrane-bound structures that were present throughout the cytoplasm. The amount of internalized HRP was directly related to the concentration of the protein in the medium, was not saturable at high concentrations of HRP, and increased with time. Endocytosis proceeded at 37 degrees C, but was abolished at 4 degrees C. In pulse-chase experiments, the quantity of internalized protein in the cells did not significantly change during the 2 hr chase period. Taken together, these findings suggest that internalization of HRP occurs by fluid-phase endocytosis, a non-receptor-mediated process, and that the protein is stable within an intracellular compartment for at least several hours.

Response of cerebral endothelial cells to hypoxia: modification by fructose-1,6-bisphosphate but not glutamate receptor antagonists

Damage to the cerebral endothelium from ischemia could exacerbate brain injury by altering vascular integrity, but little is known concerning the response of cerebral endothelial cells to hypoxia. To address this issue, cerebral capillary endothelial cells were isolated from 14-day-old rats, grown to confluence, and placed in hypoxic chambers for up to 62 h. Cells were undamaged by 24 hours of hypoxia as assessed by lactate dehydrogenase release and ethidium bromide staining, but 48 h resulted in marked damage. Hypoxia was probably exacerbated by hypoglycemia because glucose levels fell to < 1 mM by 24 h, at which point ATP levels began to fall in hypoxic cultures (3.25 +/- 1.48 nmol/mg protein; mean +/- S.D.) relative to normoxic cultures (9.52 +/- 1.41 nmol/mg protein). Cells treated with 4 mM fructose-1,6-bisphosphate (FBP) had significantly less damage at 48 h of hypoxia than controls. FBP had little effect on rate of glucose depletion from the media, but ATP depletion due to hypoxia was significantly less. Thus, the protective effect of FBP may be mediated by the ability of treated cells to maintain higher ATP levels. Unlike FBP, glutamate receptor antagonists including MK-801, NBQX, DNQX, and kynurenic acid were ineffective in ameliorating hypoxia-induced endothelial cell injury.

Calcium/calmodulin-stimulated protein kinase II is present in primary cultures of cerebral endothelial cells

Calcium/calmodulin-stimulated protein kinase II (CaM-PK II), a major kinase in brain, has been established to play an important role in neurotransmitter release and organization of postsynaptic receptors, and it is known to be involved in long-term potentiation and memory. Less is known about the function of this enzyme in nonneural cells. Here we report on the production, presence, and phosphorylation of the alpha-subunit of CaM-PK II in primary cultures of cerebral endothelial cells. These results raise the possibility that alpha-CaM-PK II can act as one of the key enzymes of calcium-mediated intracellular signaling in the cerebral endothelial cells and suggest that alpha-CaM-PK II may participate in such basic cellular processes as permeability in physiological and pathological conditions.

The cerebral microvessels in culture, an update

Recent advances in our knowledge of the blood-brain barrier (BBB) have in part been made by studying the properties and function of cerebral endothelial cells in vitro. After an era of working with a fraction, enriched in cerebral microvessels by centrifugation, the next generation of in vitro BBB model systems was introduced, when the conditions for routinely culturing the endothelial cells were established. This review summarizes the results obtained from this rapidly growing field. It can be stated with certainty that, in addition to providing a better insight into the chemical composition of cerebral endothelial cells, much has been learned from these studies about the characteristics of transport processes and cell-to-cell interactions during the last 12 years. With the application of new technologies, the approach offers a new means of investigation, applicable not only to biochemistry and physiology but also to the drug research, and may improve the transport of substances through the BBB. The in vitro approach has been and should remain an excellent model of the BBB to help unravel the complex molecular interactions underlying and regulating the permeability of the cerebral endothelium.